Technical modification of the sagittal split mandibular ramus osteotomy Loh Fun-Chee, BDS, AIDS, MSc, FAA4S,a Singapore NATIONAL

UNIVERSITY

OF SINGAPORE,

NATIONAL

UNIVERSITY

HOSPITAL

The sagittal split mandibular ramus osteotomy is a versatile surgical option for the correction of mandibular prognathism, retrognathism, and asymmetry. At the same time, it enables the use of internal rigid fixation. However, surgical complications including injury to the inferior dental neurovascular bundle and unfavorable fracture can occur. A technical modification and a concept instrumentation is suggested with the view of minimizing such complications. (ORAL

SURC ORAL MED

ORAL PATHOL

1992;74:723-6)

T

he mandibular ramus sagittal split osteotomy is a versatile surgical technique for both advancement and pushback of the mandible. Since its introduction by Schuchardt’j 2 in 1942 and by Trauner and Obwegeser3 in 1957, various modifications have been made to the original technique. 4-* Perhaps the major technique modification was that of Dal Pont,4 who advocated extending the buccal osteotomy to the body of the mandible, hence effectively increasing the area of the sagittal split. This offers the advantage of greater area of bone contact, which promotes good bony healing, especially in cases of mandibular advancement. This modification, however, increases the risk of encountering the inferior dental neurovascular bundle and the chance of fracture of the proximal and distal segments at the area of the sagittal split. Various technique of splitting the ramus have been proposed with the aim of avoiding damage to the inferior dental neurovascular bundle and unfavorable fracture of the mandibular ramus.7-10 This is a report of the technique and instrumentation I have used for the sagittal split mandibular ramus osteotomy. MATERIAL AND METHODS Twenty-five patients who required mandibular pushback were treated with bilateral mandibular ramus sagittal split osteotomy. Intraoperative complications such as damage to the inferior dental neurovascular bundle, unintended fracture of the proxiTonsultant, 7112138598

Department

of Oral

and Maxillofacial

in

Surgery.

ma1 segment, distal segment, or any other surgical complications were noted. Instrumentation The essential instruments used for the ramus sagittal splits are a broad chisel, measuring 2 cm wide and 4 mm thick with a curved handle (Fig. l), and a T-shaped bone cleaver (Fig. 2). Technique The technique for the soft tissue incision and bone cut are concerned is essentially similar to those previously reported. A 2 to 3 cm long retromolar linear incision is made with an electric cautery knife to reduce bleeding. The mucosal incision is placed buccal to the external oblique ridge and is directed lingually toward the external oblique ridge as the incision is deepened. This avoids exposing the buccal fat pad, which can be a nuisance to the surgeon. On the buccal aspect minimal stripping of the masseter is done. The external oblique ridge and the buccal cortical bone at the second molar area are then fully exposed. On the lingual side the mucoperiosteal flap is generously raised to expose the lingula and the bone around it. With a long Linderman bur or a reciprocating saw, the lingual horizontal osteotomy is made just above the lingula and extended about 3 mm posterior to it. The vertical buccal osteotomy is sited about the second molar area. The two osteotomies are then connected. All cuts are made through the cortical bone. Special attention is paid to the corners formed by the connecting osteotomy and the lingual and buccal os723

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ig. 1. Chisel with curved handle.

T-shaped bone cleaver. teotomies. Sufficient depth of bone must be removed from these two corners until the cancellous layer is encountered. The broad chisel is then inserted into the connecting osteotomy at the superior border with the bevel toward the lingual side. It is then rotated in counterclockwise on the right side and clockwise on the left side, to initiate the split. Simultaneously the T-shaped bone cleaver is inserted into the anterior superior corner of the proximal segment (Fig. 3,A). With the buccal cortex of the distal segment as a fulcrum, the T-shaped bone cleaver is rotated to aid the split. As the proximal and distal segments separate, the plane

of cleavage is suctioned and attention is paid to the inferior dental neurovascular bundle. In the vast majority of cases this is not encountered. The T-shaped cleaver is gradually advanced inferiorly until the inferior border of the mandible is reached (Fig. 3, B). The cleaver is then “edged” posteriorly while it remains at the inferior border and is rotated intermittently to create a gradual splitting of the inferior border of the ramus. Because the crossbar of the “T” is kept below the inferior dental neurovascular bundle, damage to the bundle is avoided. The cleaver does not have any sharp edges; therefore there is no danger to the facial soft tissues should it slip below the inferior

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Fig. 3. A, Chisel inserted at superior border and T-shaped bone cleaver at anterosuperior corner of proximal segment to initiate split. B, Superior aspect of proximal and distal segments separating and T-shaped bone cleaver is positioned at inferior border of mandible at plane of cleavage. border. The final point of bony adherence between the proximal and distal segment is at the inferior posterior part of the ramus. This is effectively separated by the rotating the cleaver at this region. On rare occasions the inferior dental neurovascular bundle is found to be on the wrong side, that is, adhering to the proximal segment. With a thin spatula osteotome the inferior dental neurovascular bundle can be freed. The proximal segment is then completely mobilized. Through the split the medial pterygoid muscle is stripped from the medial aspect of the angle of the mandible. This is important, especially in mandibular pushback cases. The mandible is then guided into the predetermined position with an occlusal wafer. In mandibular pushback cases the overlapping bone at the anterior border of the proximal segment is removed so that the proximal segment can be positioned passively against the distal segment. Rigid osteosynthesis is achieved by the use of two or three 2.7 mm bicortical screws. Care is taken to ensure that the condyle is not distracted from the articulating fossa. The incision is then closed with 3-O resorbable sutures. RESULTS Twenty-five cases of the sagittal split mandibular ramus osteotomies performed by the author were evaluated for injury to the inferior dental neurovascular bundle, fracture of the proximal segment, fracture of the distal segment, and any other complications. There was no severance of the inferior dental neu-

rovascular bundle, although in four sides (two patients) the inferior dental neurovascular bundle was on thle wrong side; that is, it adhered to the proximal segment. Fracture of the proximal segment was not encountered. In one case a partial fracture of the distal segment was associated with a deeply impacted third molar. Other forms of surgical complications were not encountered. DISCUSSION Adequate removal of the cortical bone along the osteotomy lines until the cancellous layer is reached is the most important requisite to achieving a successful and predictable sagittal split of the ramus. This step is essential because it effectively provides a cleavage plane. It is therefore important that all osteotomy cuts be checked to ensure that the marrow (as indicated by oozing of blood) is reached. The only area along the plane of cleavage where cortical bone is not weakened by cutting instrument is the inferior border of the ramus and the posterior part of the body of the mandible. Attention is needed there. The rationale of using a curved monobeveled instrument is to direct the cleaving edge of the instrument toward the buccal cortex and to attempt to create a plane of cleavage buccal to the inferior dental neurovascular bundle. The broad width ensures sufficient separation between the buccal and lingual cortices for inspection of the inferior dental neurovascular bundle after the split has been initiated superiorly. The use of the T-shaped cleaver at the anterosuperior corner of the proximal segment with one limb of the “T” in the osteotomy line and the other resting on

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the buccal cortex of the distal segment is found to be useful because the force used is distributed and hence the chance of fracture at a particular pressure point is decreased. Edging the cleaver along the anterior border of the proximal segment towards the lower border ensures a gradual splitting to occur. This process simultaneously redistributes the forces to different parts of the bone and guides the plane of split. The last remaining area of bony adherence is the inferior border. Here the T-shaped cleaver is used to edge along the inferior border and prying at the same time to complete the split. Because the cleaver is kept below the inferior dental neurovascular bundle, there is therefore no danger of injury to the structure during this maneuver. Previous reports have cited incidence of unfavorable fracture of the proximal segment ranging from 3%9, l1 to 6.6%t2 and distal segments less than 1%.9 With careful surgical technique this type of complication can be avoided. Severance of the inferior dental neurovascular bundle has previously been reported as about 3.5%.9 This mishap could happen when protection is inadequate during the osteotomy of the lingual cortex. Injury to the inferior dental neurovascular bundle can also occur if the lingual osteotomy is erroneously placed inferior to the lingula. Identification of the lingula is perhaps the most effective means to avoid this mishap. The third possibility is perhaps severance by instrumentation during the split itself. I believe that a deliberate attempt to effect the split as close to the buccal cortex as possible and to keep a watchful eye of the inferior dental neurovascular bundle during instrumentation is an important factor. Although the bundle was encountered on four occasions (two patients), there was no incidence of severance of the neurovascular bundle. CONCLUSION

This article focuses on the technical aspect of sagitally splitting the ramus of the mandible and instrumentation used. With careful instrumentation and handling of the proximal and distal segment during

ORALSURGORAL

?V~EDORALPATHOL December 1992

the ramus split, unfavorable fracture and severance of the inferior dental neurovascular bundle can be minimized. I acknowledge Prof. Peter Egyedi, formerly Head, Department of Oral and Maxillofacial Surgery, University of Utrecht, The Netherlands. REFERENCES 1. Schuchardt

2.

3.

4. 5.

K. Ein Seitrag zur chirurgischen Kieferorthopadie unter Berucksichtigue ihrer Bedeutung fur die Behandlung angeborener und erworbener Kieferdeformitaten bei Soldaten. Dtsch Zahn Mund Kieferhulkd Zentralbl 1942;9:73-89. Schuchardt K. Formen des offenen Bisses and ihre operativen Behandlungsmoglichkeiten. In: Fortschritte der Kiefer und Gesichts-chirurgie. Stuttgart: Band 1, 1955. Trauner R. Obwegeser HL. The surgical correction of mandibular prognathism and retrognathis with consideration of genioplasty. Part 1. Surgical procedures to correct mandibular prognathism and reshaping of the chin. ORAL SURG ORAL MED ORAL PATHOL 1957;10:677-89. Dal Pont G. Retromolar osteotomy for the correction of prognathism. J Oral Surg 1961;19:42-7. Hunsuck EE. A modified intraoral sagittal splitting technic for correction of mandibular prognathism. J Oral Surg 1968;26:

250-3. 6. Gallo WJ,

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Moss M, Gaul JV, Shapiro D. Modification of the sagittal ramus split osteotomy for retrognathia. J Oral Maxillofac Surg 1967;34:178-9. Epker BN. Modifications in the sagittal osteotomy of the mandible. J Oral Surg 1977;35:157-9. Wolford LM, Bennett MA, Rafferty CG. Modification of the mandibular ramus sagittal split osteotomy. ORAL SURG ORAL MED ORAL PATHOL 1987;64:146-55. Turvey TA. Intraoperative complications of the sagittal osteotomy of the mandibular ramus: incidence and management. J Oral Maxillofac Surg 1985:43:504-9. Leonard MS, Ziman k’, Beks R, et al. The sagittai split osteotomy of the mandible. ORAL SURG ORAL MED ORAL PATHOL 1985;60:459-66. Behrman SJ. Complications of sagittal osteotomy of the mandibular ramus. J Oral Surg 1972;30:554-61. Macintosh RB. Experience with the sagittal osteotomy of the mandibular ramus: a 3-year review. J Oral Maxillofac Surg 1981;8:151-65.

Reprint requests: Loh Fun-Chee, BDS, MDS, MSc, FAMS Department of Oral and Maxillofacial Surgery National University of Singapore National University Hospital Lower Kent Ridge Road Singapore 05 11

Technical modification of the sagittal split mandibular ramus osteotomy.

The sagittal split mandibular ramus osteotomy is a versatile surgical option for the correction of mandibular prognathism, retrognathism, and asymmetr...
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